"Well, I was in denial that I was even pregnant at first, so when I found out I was having twins, I just kind of laughed like, 'Of course this would happen!'" The Back-Up Plan star, 40, said at a press conference for the movie in Beverly Hills Tuesday. "And then I started giggling."

"Marc started crying," she recalls. "It was a joyous time. We were happy... He's emotional! He just couldn't believe it was happening. He'd had children before and this was like a whole new, special experience."

Now that Max and Emme are two years old, Lopez tells UsMagazine.com that they are starting to realize when she has to leave to work -- and they don't like it.

"They're at the point now where they've come to the door and started yelling, 'No, no, Mommy, don't go!' And I was like, 'Whoa, this is bad,'" she tells Us. "That's really tough. So I'm just going to have to figure it out as I go along. I keep trying to explain to them, 'I'll be home and the sun will still be out!'"

Lopez, who plays a woman who decides to get artificially inseminated in her new flick, admits she wouldn't consider being a single mom in real life.

"It's just too hard!" Lopez says. "Honestly. I have so much respect for single moms or anyone who finds themselves a single mother -- but to choose to be a single parent is courageous. It's such a hard job to raise a child and to be everything to that child without a partner... I don't know if I could do it on my own, I really don't."